1. Field of the Invention
The subject invention relates to an endocardial lead, and more particularly, to an implantable cardioversion and defibrillation lead for applying electrical energy to the heart.
2. Background of the Related Art
It is well known in the field of cardiology that certain types of cardiac arrhythmia known as ventricular tachycardia and fibrillation can be effectively treated by the application of electrical energy to the heart to defibrillate the fibrillating tissue. Implantable defibrillation leads have been developed to stimulate the heart when an arrhythmia occurs. These devices typically include electrodes that are placed adjacent to the inside wall of the heart. Electric current is applied to the electrode through an interconnected insulated electrode wire to stimulate the heart muscle which is in contact with the electrode.
In general, there are two types of endocardial lead tips. The first type is commonly referred to as a passive fixation tip and the second is known as an active fixation tip. An active fixation tip is of the screw-in type wherein a physician manually screws or engages a conductive electrode element into the heart wall. An example of a lead with a screw type fixating means is disclosed in U.S. Pat. No. 5,261,417 to Osypka. The passive fixation tip generally requires no action of the physician beyond insertion of the lead in a normal manner together with placement of the electrode tip in the apex of the ventricle. In order to stabilize the position of such a lead at the heart wall, tines made of thin wire or elastomeric material are used to entrap or hold the distal end of the lead in the trabeculae of the heart. An example of a lead with passive fixation means is disclosed in U.S. Pat. No. 4,945,922 to van Krieken.
It is preferable to have defibrillation leads that are easily implantable and which have substantially large surface areas to provide even current distribution and low energy thresholds. Thus, defibrillation leads are known which are collapsed into an advancement position for implantation in the body and subsequently deployed into an operating condition. Examples of such leads are disclosed in U.S. Pat. No. 5,282,845 to Bush et al. which defines a lead having a plurality of curvilinear electrodes, and U.S. Pat. No. 5,411,527 to Alt which defines a lead having a plurality of individual fiber strands. Neither prior art reference includes fixation means for stabilizing the position of the lead at the wall of the heart.
It would be beneficial to provide a defibrillation lead that is easily implantable, has a substantially large defibrillating surface area to provide even current distribution and low energy thresholds, and is configured for permanent active fixation at the wall of the heart.
The subject invention is directed to an implantable endocardial cardioversion and defibrillation lead for applying electrical energy to the heart which includes an elongated insulative lead body having opposed proximal and distal end portions, and having a lumen extending therethrough. An electrode assembly is operatively associated with the distal end portion of the lead body. The electrode assembly has a defibrillating surface for stimulating cardiac tissue and includes a distal tip electrode having a central annular portion and circumferentially disposed structural means extending radially from the central portion to define the area defibrillating surface.
A connector assembly is operatively associated with the proximal end portion of the lead body for facilitating electrical connection to an implanted automated defibrillator or a similar energy producing device. A coiled multifilar conductor assembly extends through the lumen of the lead body to electrically join the electrode assembly and the connector assembly.
In accordance with a preferred embodiment of the subject invention, the structural means extending radially from the central annular portion of the distal electrode tip is defined by a plurality of circumferentially spaced apart radially extendable arms. The arms are adapted and configured for movement between a first position wherein they are in an axially extended orientation (i.e., constrained within the tubular sheath of an introducer) and a second position wherein they are in a radially extended orientation. It is envisioned that the radially extendable arms can vary in configuration and number, and that they may be rearwardly or forwardly (proximally or distally) swept during percutaneous introduction.
The electrode assembly can include as few as three or as many as six or more circumferentially spaced apart radially extendable arms. Furthermore, the arms may be constructed from flat strips of material or from round wire stock. The electrode assembly is preferably formed from a bio-compatible metal selected from the group consisting of platinum, iridium, platinum-iridium alloy, tantalum, and titanium. Alternatively, the arms may be formed from a shape memory alloy, such as, for example, a titanium-nickel alloy which will aide in the movement of the arms from a constrained position to a deployed position.
The elongated insulative lead body can have a generally linear configuration, or a preformed J-shaped configuration depending upon intended use, i.e., right ventricular or a trial implantation. The insulative lead body is preferably formed from a non-conductive material selected from the group consisting of polyurethane and silicone. It is envisioned that the lead may be configured for defibrillation, sensing or pacing in either a unipolar, bipolar or tripolar mode.
In a preferred embodiment of the subject invention, the lead includes a retractable fixation screw operatively associated with the distal end portion of the lead body for securing the lead assembly to cardiac tissue. Alternatively, the fixation screw may be stationary relative to the lead body. Preferably, the fixation screw is electrically active and forms part of the distal electrode assembly. However, it is envisioned that the fixation screw may be electrically insulated from the electrode assembly so as not to contribute in whole or in part to the electrode surface of the lead. In this instance, the screw would serve as a sensing pathway for the lead.
The subject invention is also directed to a method of implanting an endocardial lead which includes the step of introducing an endocardial defibrillation lead having an elongated lead body with an electrode assembly operatively associated with a distal end portion thereof, the electrode assembly and include a plurality of radially extendable arms configured for movement between an axially extended orientation and a radially extended orientation. The method further includes the step of moving the radially extendable arms from the axially extended orientation to the radially extended orientation. The method also includes the steps of providing a tubular introducer sheath for percutaneously introducing the lead and actively securing the distal end of the lead to cardiac tissue.
These and other unique features of the endocardial defibrillation lead of the subject invention and the method of constructing and using the same will become more readily apparent from the following description of the drawings taken in conjunction with the detailed of the preferred embodiments.